1. Field of the Invention
The present invention is related to a total reflection illuminated sensor chip, which is employed in a method for detecting substances within samples by utilizing evanescent waves.
2. Description of the Related Art
Conventionally, detecting methods that utilize evanescent waves or surface plasmon induced by totally reflected illumination are being focused on, in biological measurements for detecting proteins, DNA, and the like. Surface plasmon are compression waves of free electrons which are generated by the free electrons vibrating as a group at the surfaces of metals. Such detecting methods include SPFS (Surface Plasmon Field enhanced fluorescence Spectroscopy) measurement and SPR (Surface Plasmon Resonance) measurement, which employs attenuated total reflection due to surface plasmon resonance.
SPFS measurement is a method in which detection target substances are detected, by: generating evanescent waves on a metal film that functions as a detecting portion provided on a dielectric prism; exciting the detection target substances included in samples or fluorescent labels attached to the detection target substances by the evanescent waves; and detecting the fluorescence emitted by the detection target substance or the fluorescent labels (refer to Japanese Patent No. 3562912). The evanescent waves are generated on the metal film, by causing a measuring light beam to be totally reflected at the interface between the dielectric prism and the metal film provided thereon. SPFS measurement is easy to execute, and is capable of measuring a plurality of samples simultaneously. Further, the electric field enhancing effect of surface plasmon, which is generated by the evanescent waves resonating with free electrons in the metal film amplify the evanescent waves, which enables great fluorescent signals to be detected. Accordingly, SPFS measurement is widely used.
Meanwhile, SPR measurement is a method in which detection target substances are detected, by: varying the incident angle of light that enters the interface between a dielectric prism and a metal film that functions as a detecting portion provided on the dielectric prism; and detecting attenuation of light reflected at the interface to detect a change in the refractive index on the metal film (refer to U.S. Patent Application Publication No. 20060159591). For example, if antigens bind with antibodies which are immobilized on the metal film by antigen antibody reactions, the refractive index on the metal film becomes greater than that of the surrounding buffer. Accordingly, SPR measurement is detects the change in refractive index as a change in the SPR resonance angle (an incident angle at which the reflected light is attenuated). SPR measurement, which is a method for detecting refractive indices, is widely used as a method that enables reactions, binding amounts and analysis of binding speeds among biological molecules in real time without labeling.
In the aforementioned SPFS measurement and SPR measurement, measuring light beams are totally reflected at interfaces between dielectric prisms and a detecting portion. Therefore, dielectric prisms, on predetermined regions of which a detecting portion are formed, are commonly employed as sensor chips. Presently, dielectric prisms formed of plastic, which are less expensive and more easily molded than glass, are commonly employed. However, during conventional measurement operations, dielectric prisms are exposed during handling of sensor chips. Therefore, there is a problem that damage and contamination occurs at the surfaces through which measuring light beams enter the dielectric prisms, or at the surfaces through which light exits the dielectric prisms. Particularly, plastic dielectric prisms are softer than those formed of glass, and therefore the surfaces thereof are more likely to become damaged. In these cases, the damage and contamination generates noise due to absorption, attenuation, and scattering of measuring light beams, and the measurement accuracy deteriorates. Therefore, U.S. Patent Application Publication No. 20060159591 teaches a sensor unit equipped with a protective member that protects the surface of a dielectric prism through which measurement light beams enter or the surface through which light exits the dielectric prism.
There is demand for diagnostic sensor chips to be produced at low cost, and to be made thinner. However, the sensor unit disclosed in U.S. Patent Application Publication No. 20060159591 has a great number of parts, and therefore does not sufficiently meet this demand. Further, it is difficult to form a sensor unit, which includes a protective member having a small slit for transmitting light therethrough, thin.